What was actually possible with the GB/CB/1912 Fast design

I originally wanted a displacement of 29,000 tons and 180,000 SHP for power. If we use figures close to those, we don't see 38 knots, but more like 34 knots:

GB/CB/1910 Fast 34 knots, Great Britain Battlecruiser laid down 1910 (Engine 1918)

Displacement:
 27,244 t light; 28,146 t standard; 30,454 t normal; 32,301 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
 (854.78 ft / 850.00 ft) x 95.00 ft x (33.00 / 34.30 ft)
 (260.54 m / 259.08 m) x 28.96 m  x (10.06 / 10.45 m)

Armament:
      4 - 13.50" / 343 mm 45.0 cal guns - 1,250.00lbs / 566.99kg shells, 90 per gun
   Breech loading guns in turret on barbette mounts, 1910 Model
   2 x Twin mounts on centreline ends, evenly spread
      16 - 4.00" / 102 mm 45.0 cal guns - 32.00lbs / 14.51kg shells, 150 per gun
   Quick firing guns in deck and hoist mounts, 1910 Model
   16 x Single mounts on sides, forward deck aft
  4 raised mounts - superfiring
      Weight of broadside 5,512 lbs / 2,500 kg

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 6.00" / 152 mm 475.00 ft / 144.78 m 16.00 ft / 4.88 m
 Ends: Unarmoured
   Main Belt covers 86 % of normal length
   Main belt does not fully cover magazines and engineering spaces

   - Torpedo Bulkhead - Additional damage containing bulkheads:
  1.50" / 38 mm 475.00 ft / 144.78 m 33.00 ft / 10.06 m
 Beam between torpedo bulkheads 64.00 ft / 19.51 m

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 8.00" / 203 mm 5.00" / 127 mm  8.00" / 203 mm
 2nd: 4.00" / 102 mm 2.00" / 51 mm  4.00" / 102 mm

   - Armoured deck - multiple decks:
 For and Aft decks: 3.00" / 76 mm
 Forecastle: 3.00" / 76 mm  Quarter deck: 3.00" / 76 mm

   - Conning towers: Forward 8.00" / 203 mm, Aft 5.00" / 127 mm

Machinery:
 Oil fired boilers, steam turbines, 
 Direct drive, 4 shafts, 182,011 shp / 135,780 Kw = 34.07 kts
 Range 6,499nm at 16.00 kts
 Bunker at max displacement = 4,155 tons

Complement:
 1,152 - 1,498

Cost:
 £2.386 million / $9.543 million

Distribution of weights at normal displacement:
 Armament: 995 tons, 3.3 %
    - Guns: 995 tons, 3.3 %
 Armour: 6,973 tons, 22.9 %
    - Belts: 1,934 tons, 6.3 %
    - Torpedo bulkhead: 870 tons, 2.9 %
    - Armament: 1,121 tons, 3.7 %
    - Armour Deck: 2,776 tons, 9.1 %
    - Conning Towers: 273 tons, 0.9 %
 Machinery: 6,566 tons, 21.6 %
 Hull, fittings & equipment: 12,710 tons, 41.7 %
 Fuel, ammunition & stores: 3,210 tons, 10.5 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   47,134 lbs / 21,380 Kg = 38.3 x 13.5 " / 343 mm shells or 5.8 torpedoes
 Stability (Unstable if below 1.00): 1.21
 Metacentric height 6.5 ft / 2.0 m
 Roll period: 15.6 seconds
 Steadiness - As gun platform (Average = 50 %): 79 %
   - Recoil effect (Restricted arc if above 1.00): 0.41
 Seaboat quality  (Average = 1.00): 1.60

Hull form characteristics:
 Hull has low quarterdeck ,
   a normal bow and a cruiser stern
 Block coefficient (normal/deep): 0.400 / 0.408
 Length to Beam Ratio: 8.95 : 1
 'Natural speed' for length: 29.15 kts
 Power going to wave formation at top speed: 48 %
 Trim (Max stability = 0, Max steadiness = 100): 49
 Bow angle (Positive = bow angles forward): 8.00 degrees
 Stern overhang: 0.00 ft / 0.00 m
 Freeboard (% = length of deck as a percentage of waterline length):
    Fore end,  Aft end
    - Forecastle: 20.00 %,  34.00 ft / 10.36 m,  31.00 ft / 9.45 m
    - Forward deck: 30.00 %,  31.00 ft / 9.45 m,  30.00 ft / 9.14 m
    - Aft deck: 17.00 %,  30.00 ft / 9.14 m,  30.00 ft / 9.14 m
    - Quarter deck: 33.00 %,  22.00 ft / 6.71 m,  22.00 ft / 6.71 m
    - Average freeboard:  27.95 ft / 8.52 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 127.1 %
  - Above water (accommodation/working, high = better): 249.2 %
 Waterplane Area: 49,706 Square feet or 4,618 Square metres
 Displacement factor (Displacement / loading): 122 %
 Structure weight / hull surface area: 166 lbs/sq ft or 808 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.95
  - Longitudinal: 1.64
  - Overall: 1.00
 Cramped machinery, storage, compartmentation space
 Excellent accommodation and workspace room
 Ship has slow, easy roll, a good, steady gun platform
 Excellent seaboat, comfortable, can fire her guns in the heaviest weather